Re: Extract part of a list

one possible solution is (if i understood the question) :


use strict;

my @notgood = qw(1 5 6 9);
my @goodarray = qw(1 2 3 4 5 6 7 8 9);
my @good;

foreach my $yes (@goodarray){
if (!grep{$_ == $yes}@notgood){
    push @good , $yes;
}
}

print "@good";
[download]

but read how grep works and you'll probably find more elegant way to do this

Comment on Re: Extract part of a list Download Code

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Re^2: Extract part of a list by blazar (Canon) on Jul 29, 2008 at 08:45 UTC
I personally believe that to expand a little bit on the subject, I may mention that that code may be cast in the form of two nested greps: `my @good = grep { my $yes = $_; !grep $_ == $yes, @notgood; } @goodarray;` [download] One minor inconvenience, with the inner one, is that it scans all of `@notgood` also when it has already found one matching element: of course we're generally not manic about this because we don't care premature optimization; but I somewhat psychologically feel uneasy with it. Then List::Util's `first()` comes to the rescue: `my @good = grep { my $yes = $_; !first {$_ == $yes} @notgood; } @goodarray;` [download] Too bad it's not a builtin in the first place. But then 5.10 can do even better, with its smart match operator: `my @good = grep { not @notgood ~~ $_ } @goodarray;` [download] And that's it! `--` If you can't understand the incipit, then please check the IPB Campaign.	[reply] [d/l] [select]

Replies are listed 'Best First'.

Re^2: Extract part of a list
by blazar (Canon) on Jul 29, 2008 at 08:45 UTC

I personally believe that to expand a little bit on the subject, I may mention that that code may be cast in the form of two nested greps:

  my @good = grep {
    my $yes = $_;
    !grep $_ == $yes, @notgood; 
} @goodarray;
[download]

One minor inconvenience, with the inner one, is that it scans all of @notgood also when it has already found one matching element: of course we're generally not manic about this because we don't care premature optimization; but I somewhat psychologically feel uneasy with it. Then List::Util's first() comes to the rescue:

my @good = grep {
    my $yes = $_;
    !first {$_ == $yes} @notgood;
} @goodarray;
[download]

Too bad it's not a builtin in the first place. But then 5.10 can do even better, with its smart match operator:

my @good = grep { not @notgood ~~ $_ } @goodarray;
[download]

And that's it!

--
If you can't understand the incipit, then please check the IPB Campaign.

[reply]
[d/l]
[select]